This invention is in the field of electrographic printing, and is more specifically directed to the electrographic printing of documents suitable for reading by Magnetic Ink Character Recognition (MICR) technology.
Electrographic printing has become the prevalent technology for modem computer-driven printing of text and images, on a wide variety of hard copy media. This technology is also referred to as electrographic marking, electrostatographic printing or marking, and electrophotographic printing or marking. Conventional electrographic printers are well suited for high resolution and high speed printing, with resolutions of 600 dpi (dots per inch) and higher becoming available even at modest prices. As will be described below, at these resolutions, modem electrographic printers and copiers are well-suited to be digitally controlled and driven, and are thus highly compatible with computer graphics and imaging.
A typical electrographic printer includes a primary image forming photoconductor, which may be a moving belt in large scale printers, or a rotating drum in smaller laser printers and photocopiers. The photoconductor is initially sensitized or conditioned by the application of a uniform electrostatic charge at a primary charging station in the printer. An exposure station forms an image on the sensitized photoconductor by selectively exposing it with light according to the image or text to be printed. The exposure station may be implemented as a laser, an array of light emitting diodes (LEDs), or a spatial light modulator. In modem electrographic printing, a computer typically drives the exposure station in a raster scan manner according to a bit map of the image to be printed. The exposing light discharges selected pixel locations of the photoconductor, so that the pattern of localized voltages across the photoconductor corresponds to the image to be printed.
At a developing or toning station in the typical electrographic printer, a developer roller or brush is biased to a bias voltage roughly at the primary charging voltage of the sensitized photoconductor prior to exposure. The biased developer roller or brush is loaded with toner charged to the bias voltage. As the exposed photoconductor passes the developing station, toner is attracted to the discharged pixel locations of the photoconductor. As a result, a pattern of toner corresponding to the image to be printed appears on the photoconductor.
The typical electrographic printer transfers the pattern of toner from the photoconductor to the printed medium (e.g., paper) at a transfer station. The transfer station charges the medium to an opposing voltage, so that the toner on the photoconductor is attracted to the medium, as the medium is placed in proximity to the photoconductor. Heat is then applied to the medium to fuse the transferred toner, and the medium is discharged and ejected from the printer. The photoconductor is then cleaned of any residual toner, and is prepared for the next image.
Magnetic Ink Character Recognition (MICR) technologies have been used for many years for the automated reading and sorting of checks and negotiable payment instruments, as well as for other documents in need of high speed reading and sorting. As well known in the art, MICR toner is a mixture of a fine metallic powder with polyester resin and powdered dye and MICR documents are printed with characters in a special font (e.g., the E13-B MICR font in the United States, and the CMC-7 MICR standard in some other countries). Typically, MICR characters are used to indicate the payor financial institution, payor account number, and instrument number, on the payment instrument. In addition to the special font, MICR characters are printed with special inks or toners that include magnetizable substances, such as iron oxide, that can be magnetized in the reading process. The magnetized MICR characters present a magnetic signal of adequate readable strength to the reading and sorting equipment, to facilitate automated routing and clearing functions in the presentation and payment of these instruments.
The relatively heavy loading of iron oxide in conventional MICR toner for electrographic MICR printing has been observed to adversely affect the image quality of the printed characters, however. It is difficult to achieve and maintain an adequate dispersion of the heavy iron oxide particles in the toner resin. In addition, the toning and fusing efficiencies of MICR toners are poorer than normal (i.e., non-MICR) toners, because of the magnetic loadings present in the MICR toner. Accordingly, the image quality provided by MICR toner is often poorer than those formed by normal toner, unless the printing machine makes significant adjustments in its printing process.
Many documents having MICR characters also include printed features and characters that are not MICR characters. This of course requires either two printing passes (one pass for MICR printing using MICR toners and another pass for the non-MICR printing using normal toners), or the printing of both the MICR and non-MICR features with MICR toners. In some installations, the MICR printing volume is sufficient that one electrographic printer is dedicated to the printing of the MICR characters on all documents, with other printers used to print the non-MICR features on those documents. In other installations, the MICR encoded volume is less than the capacity of one printer. Some conventional electrographic printing systems permit the swapping of toning stations, so that the operator can switch between MICR and normal toners, for printing MICR and non-MICR documents, respectively.
As noted above, MICR characters are used for the printing of sensitive information such as financial institution routing numbers, and account numbers. Unauthorized use of these numbers on payment documents can facilitate fraud and theft. As such, MICR printing is preferably carried out in reasonably secure environments, by trusted human operators.
It has been observed, in connection with this invention, that the differences between MICR toners and normal toners, particularly in the developing or toning process of electrographic printing, require different operational settings for optimal image formation using MICR toners from the operational settings for optimal image formation using normal toners. Accordingly, the operator ought to change the operational settings of the electrographic printer as he or she swaps toning stations to change between MICR and normal toners.